For those interested in the details - it requires your *designated* contact to have two things:
1) An access key that is generated when you choose the contact (you are able to choose more than one). - presumably this is protecting your data.
2) Your death certificate.
The data is limited to iCloud stored data, and includes:
photos, notes, mail, contacts, calendars, reminders, iMessages, call history, iCloud Drive files, health data, voice memos, safari bookmarks/reading list, and your iCloud backups.
Licenced media, in-app purchases, payment info/apple pay, iCloud Keychain (inc. passwords).
You can choose to text message your designated user(s) a code, or print a copy to include in your estate documents. It *does not* require the user to have an iOS/MacOS device.